(1) Field of the Invention
The present invention relates to a learning and control apparatus for feedback control of an air-fuel ratio, an idle rotation number or the like in an electronically controlled internal combustion engine.
(2) Conventional Techniques
As the conventional learning and control apparatus for an internal combustion engine, there can be mentioned an apparatus for learning and control of an air-fuel ratio, as disclosed in Japanese Patent Application Laid-Open Specification No. 203828/74, and an apparatus for learning and control of an idle rotation number, as disclosed in Japanese Patent Application Laid-Open Specification No. 211738/84.
The conventional techniques will now be described with reference to an apparatus for learning and control of a base air-fuel ratio, in which the air-fuel ratio is feedback-controlled to a theoretical air-fuel ratio as an aimed control value in an internal combustion engine provided with an electronically controlled fuel injection apparatus.
An electronically controlled fuel injection valve is opened by a driving pulse signal (injection pulse) given synchronously with the rotation of an engine and while the valve is opened, a fuel is injected under a predetermined pressure.
Accordingly, the injection quantity of the fuel depends on the period of opening of the valve, that is, the injection pulse width. Assuming that this pulse width is expressed as Ti and is a control signal corresponding to the injection quantity of the fuel, Ti is expressed by the following equations: EQU Ti=Tp.times.COEF.times..alpha.+Ts and Tp=K.times.Q/N
wherein Tp stands for the injection pulse width corresponding to the basic injection quantity of the fuel, which is called "basic fuel injection quantity" for convenience, K stands for a constant, Q stands for the flow quantity of air sucked in the engine, N stands for the rotation speed of the engine, COEF stands for various correction coefficients for correcting the quantity of the fuel, which is expressed by the following formula: EQU COEF=1+Ktw+Kas+Kai+Kmr+Ketc
in which Ktw stands for a coefficient for increasing the quantity of the fuel as the water temperature is lower, Kas stands for a correction coefficient for increasing the quantity of the fuel at and after the start of the engine, Kai stands for a correction coefficient for increasing the quantity of the engine after a throttle valve arranged in an intake passage of the engine is opened, Kmr stands for a coefficient for correcting the air fuel mixture, and Ketc stands for other correction coefficient for increasing the quantity of the fuel, .alpha. stands for an air-fuel ratio feedback correction coefficient for the feedback control (.lambda. control), described hereinafter, of the air-fuel ratio of the air-fuel mixture, and Ts stands for the quantity of the voltage correction for correcting the change of the flow quantity of the fuel injected by the fuel injection valve, which is caused by the change of the voltage of a battery.
In short, the desired injection quantity of the fuel is obtained by multiplying the basic fuel injection quantity Tp by various correction coefficients COEF, and when a difference is brought about between the aimed control value to be attained by the control and the actual controlled value, this difference is multiplied by .alpha. to effect the feedback control and the correction for the power source voltage is added to the feedback control.
This air-fuel ratio feedback correction control is disclosed in, for example, U.S. Pat. No. 4,284,050, U.S. Pat. No. 3,483,851 and U.S. Pat. No. 3,750,632.
However, in this air-fuel ratio feedback control, for example, when one constant driving region is greatly changed to a different constant driving region, if the base air-fuel ratio in this different stationary driving region is greatly deviated from .lambda.=1 (.lambda. stands for an actual air-fuel ratio), it takes too long a time to perform the feedback control (proportion and integration control . . . PI control) of the change of the base air-fuel ratio generated by this deviation to .lambda.=1. More specifically, even though the base air-fuel ratio has been obtained from the specific injection quantity Tp.times.COEF and the deviation of this air-fuel ratio from the theoretical air-fuel ratio has been corrected by the PI control based on .alpha., since the base air-fuel ratio is greatly changed, the base air-fuel ratio is controlled to a value greatly different from .lambda.=1 if Tp.times.COEF used up to this time is still used, and the feedback correction by similar PI control should be performed and it takes a long time to correct the base air-fuel ratio to .lambda.=1 by the feedback correction.
A control system in which the above-mentioned disadvantage is eliminated by learning the control quantity controlled by the system and increasing the respondency of the air-fuel ratio control in the same driving state has been proposed by us in Japanese Patent Application Laid-Open Specifications No. 203828/74 and No. 203829/74 and U.S. patent application Ser. No. 604,025, filed Apr. 26, 1984, now U.S. Pat. No. 4,615,319, issued Oct. 7, 1986.
According to this control system, learning control of the air-fuel ratio feedback control is first carried out. More specifically, in the air-fuel ratio feedback control region, if the base air-fuel ratio is deviated from the aimed air-fuel ratio .lambda.t, since the feedback correction coefficient .alpha. is increased for compensating this gap during the process of transfer, the driving state at this time and .alpha. are detected, and a learning correction coefficient Kl based on this .alpha. is determined and stored. When the same driving state is brought about, the base air-fuel ratio is corrected to the aimed air-fuel ratio .lambda.t with a good respondency by the stored learning correction coefficient Kl. Storing of the learning correction coefficient Kl is performed for all of engine-driving state areas of a predetermined range formed by lattice division of a map of RAM according to the rotation speed of the engine and the engine-driving conditions such as the load.
More specifically, the map of the learning correction coefficient Kl corresponding to the rotation speed of the engine and the driving conditions of the engine such as the load is formed on RAM, and when the injection quantity Ti is calculated, the basic injection quantity Tp is corrected by Kl as shown by the following equation: EQU Ti=Tp.times.COEF.times.Kl.times..sub..alpha. +Ts (1)
Learning of Kl is advanced according to the following procedures.
(i) The engine-driving state in the constant state and the median .alpha.c of control of .alpha.(the mean value of a plurality of values Kl at the time of reversion of increase and decrease of the output signal of an O.sub.2 sensor) are detected.
(ii) The value Kl(old) heretofore learned, corresponding to the engine-driving state, is retrieved.
(iii) The value of Kl(old)+.DELTA..alpha./M is determined from c and Kl(old), and the storage is renewed with the obtained value (learned value) being as new Kl(new).
Incidentally, .DELTA..alpha. stands for the deviation from the standard value .alpha.1 and expressed by .DELTA..alpha.=.alpha.-1. The standard value .alpha.1 ordinarily set at 1.0 as the value corresponding to .lambda.=1. M is a constant larger than 1.
An apparatus for learning and control of the idle rotation speed is applied to the case where an idle control valve is disposed in an auxiliary air passage bypassing a throttle valve and the opening degree of this idles control valve is adjusted to control the idle rotation speed. When the basic opening degree of the idle control valve corresponding to the aimed idle rotation speed for each temperature of cooling water for the engine is feedback-controlled while comparing the aimed idle rotation speed with the actual idle rotation speed, a map of learning correction quantities is formed according to the temperature of cooling water as a parameter of the engine driving state, the deviation of the feedback correction quantity from the base value is learned to correct the learning correction quantity, and the basic opening degree of the valve is corrected by this learning correction quantity to stabilize the control.
According to the above-mentioned learning and control system, writing in the map for storing learning correction quantities performed without interpolation. This is because the speed of advance of learning is reduced since the learning correction quantities to be written by means of the manner of interpolation is influenced by the quantities stored in adjacent engine driving region.
In this case, however, in the driving state near the boundary between a driving region having a high degree of advance of learning (hereinafter referred to as "learned region") and a region having a low degree of advance of learning (hereinafter referred to as "unlearned region"), the control quantity is varied because the difference of the learning correction quantity between said two regions is large, and therefore, no stable control capacity can be obtained.
It is a primary object of the present invention to eliminate needless or harmful variations of the control state in the vicinity of the boundary between adjacent regions where learning correction quantities are stored.
Another object of the present invention is to eliminate needless or harmful variations of the learning state in the vicinity of the boundary between the adjacent regions where learning correction quantities are stored.
Another object of the present invention is to provide such a hysteresis that lattice axes in a memory map being stored learning correction quantities therein are shiftable according to the direction of change of the parameter of the engine driving state. The lattice axes divide a memory map into plural engine driving regions. When one of the learning correction quantities is retrieved from the memory map, the corresponding engine driving region is restricted by the shifted lattice axes with the hysteresis for obtaining the above described two objects of the present invention.
In the present invention, the lattice axes may be shiftable in such a direction that the engine driving region where the present learning correction quantity is retrieved is expanded when retrieving the engine driving region is to be in a tendency to change the present region to the adjacent region.
In the present invention, the lattice axes may also shiftable in such a direction that the engine driving condition is increased when the learning correction quantity is retrieved according to increasing of the engine driving state.
More specifically, according to the present invention, in order to attain the above objects, the learning and control apparatus of the present invention comprises the following means (A)through (I), as shown in FIG. 1.
(A)basic control quantity setting means for setting a basic control quantity corresponding to an aimed control value of the internal combustion engine, (B)reloadable memory means for storing lattice axes for dividing the engine driving state into a plurality of regions by a parameter of the engine driving state and learning correction quantities for correcting said basic control quantity for the respective regions restricted by said lattice axes, (C)learning correction quantity retrieving means for retrieving the learning correction quantity of the corresponding region from said memory means based on the actual engine driving state, (D)feedback correction quantity setting means for comparing the aimed control value with the actual value and setting a feedback correction quantity for correcting said basic control value by increasing or decreasing the feedback correction quantity by a predetermined quantity so that the actual value is brought close to the aimed control value, (E)control quantity computing means for computing a control quantity from the basic control quantity set by said basic control quantity setting means, the learning correction quantity retrievied by said learning correction quantity set by said feedback correction quantity setting means, (F)control means operated according to said control quantity to control the aimed control value, (G)learning correction quantity correcting means for learning a mean value of the deviation of the feedback correction quantity from the basic value and correcting and rewriting the learning correction quantity corresponding to the region of the existing engine driving state in such a direction as reducing said mean value, (H)driving state change direction judging means for judging the direction of change of the parameter of the engine driving state, and (I)driving region judging means for judging the driving region in which the learning correction quantity retrieved from the memory means by said learning correction quantity retrieving means is stored, with a certain hysteresis produced by shifting the driving region-defining lattice axes in a corresponding different direction with respect to each of two opposite directions of change of the parameter of the engine driving state.
According to the general construction of the present invention, the basic control quantity setting means sets a basic control quantity corresponding to an aimed control value of an air-fuel ratio, an idle rotation speed or the like, for example, according to a predetermined calculation formula or by retrieving, the learning correction quantity retrieving means retrieves a learning correction quantity of a region corresponding to the actual engine driving state from memory means, and the feedback correction quantity setting means compares the aimed control value with the actual value and sets the feedback correction quantity by increasing or decreasing the feedback correction quantity by a predetermined quantity, for example, based on the proportional integration control, so that the actual value is brought close to the aimed control value. The control quantity computing means computes the control quantity by correcting the basic control quantity by the learning correction quantity and also by the feedback correction quantity, and according to this control quantity, the control means is operated to control, for example, the fuel injection quantity or the quantity of auxiliary air for idling, and to control the air-fuel ratio or the idle rotation speed.
The memory means stores the engine driving state in a plurality of regions defined by at least 1 or 2 parameters in the state where the learning correction quantity is reloadable. In retrieving the learning correction quantity, the direction of change of the parameter of the engine driving state is judged by the driving state change direction judging means, and when the parameter is changed in one direction or in the opposite direction, the positions lattice axes defining the driving region having the learning correction quantity stored therein are shifted in the corresponding defferent direction and in this state, the driving region where said retrieving is effected is judged and the learning correction quantity is retrieved based on the result of said judgement.
In the above-mentioned system, even when the driving state is in the vicinity of the lattice axes, hunting of the control quantity, which is due to the high digree of difference between the learning correction quantities retrieved from adjacent driving regions, can be prevented, and the center of the region where learning is performed can be made substantially in agreement with the center of the driving region corrected by the judgement. Accordingly, a good learning control capacity can be maintained.
The above-mentioned object and structure of the present invention will become more apparent from the following description concerning embodiments .